A vast amount of information about edible (and not so edible) plants.
http://www.eattheweeds.com/Usually a good description of each plant and pictures for identification.
I you have the time and disk space, saving the site to your local drive would be a good addition to your prepper documents.
The website author also sells a set of DVDs with videos (only) of many forage-able plants.
DO not the disclaimer at the bottom of the page. Some plants have multiple physiological effects and you need to be aware of these before ingesting them.